Optical module, and method of mounting a phototransducer element on a circuit board to be used in said module

Abstract: An optical module comprises a plastic package (10) constituted by a package main body (12) and a cover (14), sleeves (30,31) formed integrally with the package main body (12), a circuit board (20) held in the package main body (12), light-activated elements fixed at predetermined positions of the circuit board (20), three projections (50) to (52) formed integrally with an inner surface of the package main body (12) and brought into contact with a periphery of the circuit board (20) to position the circuit board (20) and springs (54 to 56) formed integrally with an inner surface of the package (10) to press the periphery of the circuit board (20) against the projections. Since the sleeves (30,31) and the package main body (12) are integrally formed by plastic molding, the number of components is reduced, thereby simplifying the assembling steps.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an optical module used in an optical communication system such as an optical data link or an optical local area network (LAN), which uses light as an information transmission medium. Related Background Art As optical modules used in an optical communication system, there are a transmission module using an element such as an LED or a semiconductor laser as an electrooptic converting element (light-emitting element), and a reception module using an element such as a pin-photodiode as a photoelectric converting element (light-receiving element). Such an optical module generally has an element such as a light-emitting element or a light-receiving element, electronic components electrically connected to the element and arranged on a circuit board, a lens system, and a sleeve in which the end portion of an optical fiber is inserted. For an optical fiber with a fiber core having a diameter of several ten µm, the element, the lens system, and the sleeve must be assembled at high precision. For this reason, an optical module as shown in Fig. 1 is conventionally used. The optical module shown in Fig. 1 has a cylindrical holding body 1. The holding body 1 is formed of a metal such as stainless steel. A lens (not shown) is arranged in the holding body 1 at one end. The other end portion of the holding body 1 serves as a sleeve for receiving a ferrule (not shown) at the end portion of an optical fiber. A phototransducer element 2 is fixed to the holding body 1 with an adhesive or the like. The element 2 is arranged such that the optical axes of the element 2, the ferrule connected to the holding body 1 and the lens are matched with each other. The holding body 1 having the element 2 fixed therein is supported, together with a circuit board 3, by a package main body 4 consisting of a ceramic or metal. The terminals of the element 2 are connected by soldering (not shown) to electronic components 5 such as bare chip ICs mounted on the circuit board 3. The package main body 4 has inner lead pins 6 mounted inside the body 4, and outer lead pins 7 mounted outside the body 4 and electrically connected to the inner lead pins 6. The inner lead pins 6 are electrically connected to terminals on the circuit board 3 by soldering. The wiring pattern and the electronic components 5 are sealed by a lid 8. Finally, a cover 9 is fixed to the package main body 4, thereby completing the optical module. In the conventional optical module as described above, the phototransducer element 2 is held by the holding body 1 formed of a metal cylinder. The holding body 1 is an independent member separate from the package main body 4 having the circuit board 3 mounted thereon and the cover 9. For this reason, there are many components of the module, resulting in higher production cost and lower production efficiency. Although not illustrated, an optical module is known in which a lead frame is used in place of a package main body and a cover. A circuit board and a phototransducer element are mounted in the lead frame, and all these components are integrally molded with a plastic (Japanese Utility Model Laid-Open No. 2-126107). In this case, however, the phototransducer element and the circuit board are independent members, as in the optical module shown in Fig. 1. Therefore, the same problem as in Fig. 1 is present. EP 0 320 214 A3 discloses an optical module according to the preamble of claim 1 and having a zinc die cast housing. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an optical module which can be easily and precisely assembled without using a cylindrical metal holding body. The object is achieved by an optical module according to claim 1, with preferred embodiments thereof indicated in the dependent claims. In order to achieve the above object, according to the present invention, the constituent components of an optical module are integrally formed of a plastic. In this case, it is important to check whether an element such as a light-emitting element or a light-receiving element, a lens, and a sleeve can be precisely arranged by plastic molding. The present inventor made an examination based on Fig. 2 and found that the precision required to couple light with a quartz optical fiber (graded-index type, core diameter: 62.5 µm) could be ±15 µm in a plane perpendicular to the optical axis and ±50 µm in a direction parallel to the optical axis. It was confirmed that, with this precision, the optical module could be realized with the dimensional precision of the plastic molding. Fig. 2 is a graph showing the relationship between a deviation in optical axis and the coupled optical power wherein the quartz optical fiber and the phototransducer element are separated from each other by a predetermined interval. This graph was obtained in the following manner. Two lenses were arranged between an end of the optical fiber and the phototransducer element. The lens far from the end face of the optical fiber was defined as the first lens, and the lens closer to the end face of the optical fiber was defined as the second lens. The first lens was fixed, and the second lens was stationary with respect to the optical axis. In this state, the second lens was moved in the plane perpendicular to the optical axis, and variations in optical power of light coupled to the optical fiber were checked. Referring to Fig. 2, L1 represents an interval between the first lens and the second lens, and L2 represents an interval between the second lens and the optical fiber. Fig. 2 shows variations in power of light in five arrangements obtained upon changing the position of the second lens along the optical axis. As described above, the present inventor found, from graphs indicated by symbolsΔ and ⋄, that a dimensional precision of ±15 µm was allowed in the plane perpendicular to the optical axis, and a dimensional precision of ±50 µm was allowed in the direction parallel to the optical axis. The present invention has been made on the basis of this examination. According to the present invention, there is provided an optical module having the features necited in claim 1. In the optical module having the above arrangement, since the sleeve and the housing are integrally formed by plastic molding, the number of components is reduced, thereby simplifying the assembling steps. The circuit board is always supported by the projections at the predetermined reference points. Therefore, when the phototransducer element is arranged at the predetermined position with respect to the reference points, the phototransducer element, the sleeve, and the lens are coaxially arranged. According to the present invention, there is also provided a method according to claim 14. When the phototransducer element is to be arranged on the circuit board, the positions where the circuit board is brought into contact with the projections in the housing, i.e., the reference points can be easily specified by using the board supporting table having the positioning pins arranged in the same layout as that of the projections. As a result, the phototransducer element can be arranged at a position where it is aligned with the sleeve and the lens. The present invention will become more fully understood from the detailed description given hereinbelow and the attached drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS In the course of the following detailed description, reference will be made to the attached drawings in which: Fig. 1 is an exploded perspective view showing a conventional optical module; Fig. 2 is a graph showing variations in optical power or coupling power caused by a deviation in optical axis; Fig. 3 is an exploded perspective view showing an optical module according to a preferred embodiment of the present invention; Fig. 4 is a partially cutaway plan view showing the optical module shown in Fig. 3 in a disassembled state; Fig. 5 is a front view showing the optical module taken along a line V - V in Fig. 4; Fig. 6 is a rear view showing the rear surface of a package main body of the optical module taken along a line VI - VI in Fig. 4; Fig. 7 is a sectional view taken along a line VII-VII in Fig. 4; Fig. 8 is an enlarged perspective view showing a sleeve; Fig. 9 is a perspective view showing a method of arranging a phototransducer element on a circuit board; Fig. 10 is a perspective view showing an optical module according to another embodiment of the present invention; Fig. 11 is a perspective view showing the optical module in Fig. 10, when viewed from a lower surface side; Fig. 12 is a perspective view showing a housing and a circuit board of the optical module in Fig. 10; and Fig. 13 is a perspective view showing a method of assembling the optical module in Fig. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as "front", "rear", "left", "right", "upper", and the like, are words of convenience and are not to be construed as limiting terms. Figs. 3 to 7 are views showing an optical module according to an embodiment of the present invention. This optical module is of a transceiver type which integrates a transmission unit and a reception unit. Referring to Fig. 3, reference numeral 10 designates an entire optical module formed by plastic molding. The module 10 comprises a housing 12 and a cover 14 and serves as an optical connector receptacle for receiving, at the open front end portion thereof, connector plugs (not shown) provided at the end portions of transmission and reception optical fibers (not shown) to be connected. A circuit board 20 having ICs (not shown), a light-emitting element 16, a light-receiving element 18, and the like fixed thereon can be mounted in the module 10, at the rear end portion thereof. The housing 12 is of a rectangular prism shape or parallelepiped box shape and has a pair of side plates 22 and 23 arranged parallel to each other, an upper plate 24 and a bottom plate 26. The upper and bottom plates 24 and 26 are arranged between the upper edges and between the lower edges of the side plates 22 and 23, respectively, to be parallel to each other. As is apparent from Fig. 7, the side plates 22 and 23 and the upper plate 24 have almost the same length. The bottom plate 26 is shorter than the side plates 22 and 23 and the upper plate 24. The rear end of the bottom plate 26 is separated from the corresponding rear ends of the side plates 22 and 23 and the upper plate 24 by a predetermined distance. A transverse plate or wall 28 is arranged between the side plates 22 and 23 to perpendicularly extend from the rear end of the bottom plate 26 to the upper plate 24. Therefore, the rear end portion of the housing 12 is closed by the transverse plate 28. The other, front end portion of the housing 12 is open. The connector plugs supporting the corresponding optical fibers are inserted into said open front end portion. The side of open end portion is conveniently referred to as the front side hereinafter. The side plates 22 and 23, the upper plate 24, the bottom plate 26, and the transverse plate 28 are integrally formed of an appropriate plastic material. A pair of sleeves 30 and 31 are arranged in the package main body 12 to receive the ferrules (not shown) at the end portions of the optical fibers and align each ferrule with the light-emitting element 16 or the light-receiving element 18 (to be described later). The sleeves 30 and 31 are parallelly arranged in the longitudinal direction to be separated from each other by a predetermined interval and extend forward (i.e. in direction of the front side of the housing 12) from the front surface of the transverse plate 28. The sleeves 30 and 31 consist of the same plastic material as that of the transverse plate 28 and the like and are integrally formed on the transverse plate 28. Through-apertures or holes 32 and 33 are formed in the transverse plate 28 at portions opposing the hollow portions of the sleeves 30 and 31. Together with the hollow portions of the sleeves 30 and 31, the through-apertures 32 and 33 form continuous holes which communicate between the front inner portion and the rear inner portion of the housing body 12. When the connector plugs of the optical fibers are inserted into the housing 12 and held therein, the ferrules of the optical fibers are inserted into the corresponding sleeves 30 and 31 and supported by the inner surfaces of the sleeves 30 and 31 at desired positions. In the present invention, the sleeves 30 and 31 are not formed of a metal but a plastic, so the inner surfaces of the sleeves 30 and 31, which are in contact with the metal or ceramic ferrules, can be worn upon attachment and detachment of the connector plugs. Particularly, the inner surfaces of the sleeves 30 and 31 must be precisely formed to determine the radial positions of the ferrules. For this reason, friction between the sleeves 30 and 31 and the ferrules is increased. In this embodiment, to prevent or reduce the friction on the inner surfaces of the sleeves 30 and 31, a plurality of grooves 34 extending in the axial direction are formed in the inner surfaces of the sleeves 30 and 31, especially at portions in contact with the ferrule, and circumferentially spaced to each other, as shown in Fig. 8. With this arrangement, the contact area with respect to the ferrule is reduced, slidability is improved, and the wear of the contact surface is reduced. In addition, a tapered portion 36 is preferably provided in the inner surface of the front end portion of the sleeve so that the ferrule can be smoothly inserted into the sleeve 30 or 31. Lenses 38 and 39 are respectively arranged inside the sleeves 30 and 31, more particularly, at appropriate locations of the portions of the sleeves on which the ferrules do not abut. The lenses 38 and 39 are positioned such that their optical axes match the longitudinal axes of the corresponding sleeves 30 and 31, respectively. The lens 38 mounted in the sleeve 30 opposing the light-emitting element 16 focuses light from the light-emitting element 16 on the central portion of the end face of the corresponding ferrule, i.e., the end face of the fiber core. The condensor lens 39 mounted in the sleeve 31 focuses light emerging from the end face of the reception optical fiber on the light-receiving surface of the light-receiving element 18. The substantially rectangular circuit board 20 is arranged in a recessed portion (a portion defined by the inner surfaces of the side plates 22 and 23, the inner surface of the upper plate 24, and the rear surface of the tranverse plate 28) or necess 40 on the rear side of the housing 12, substantially parallel to the tranverse plate 28 The circuit board 20 in this embodiment consists of a ceramic, an epoxy resin, or the like. A wiring pattern (not shown) is formed on the surface of the circuit board 20, and electronic components (not shown) such as ICs are mounted thereon. As shown in Fig. 3, the wiring pattern on the circuit board 20 is electrically connected to an external circuit by a plurality of lead pins 42 extending from the lower edge of the circuit board 20. In this embodiment, the light-emitting element 16 such as a semiconductor laser or a light-emitting diode and the light-receiving element 18 are mounted on the front surface of the circuit board 20 as phototransducer elements. The light-emitting element 16 and the light-receiving element 18 are mounted on the circuit board such that the centers of the light-emitting and light-receiving surfaces almost match the central axes of the corresponding sleeves 30 and 31 when the circuit board 20 is arranged at a predetermined position in the recessed rear portion 40 of the housing 12. As is well known, in order to improve optical coupling efficiency between the light-emitting element 16 and the corresponding optical fiber, it is preferable to arrange a microball lens (not shown) at the center of the light-emitting surface of the light-emitting element 16 and fix it with a transparent adhesive or the like. Alternatively, a light-emitting element having a monolithic lens may be used. A transparent lid 44 of a plastic is fixed on the front surface of the circuit board 20 by an adhesive. The wiring pattern, the electronic components, and the phototransducer elements 16 and 18 on the front surface of the circuit board are thus shielded from the atmosphere by the lid 44. The transparent lid 44 has a rectangular flat plate portion 46 which is slightly smaller than the circuit board 20, and a peripheral portion 48 formed integrally with the peripheral edges of the flat plate portion 46 and perpendicularly depending therefrom. The end face of the peripheral portion 48 of the transparent lid 44 is bonded to the surface of the circuit board 20. Therefore, a space is formed between the flat plate portion 46 of the transparent lid 44 and the surface of the circuit board 20, and the phototransducer elements 16 and 18 and the like are arranged in this space. As described above, the circuit board 20 is arranged in the recessed 40 on the rear side of the housing 12. The circuit board 20 is accurately positioned by three positioning projections 50 to 52 formed on the inner surface of the package main body 12. As is apparent from Fig. 6, one (50) of the projections 50 to 52 is formed in the longitudinal direction on the rear side of the inner surface of the side plate 23, and the two remaining projections 51,52 are arranged in the longitudinal direction on the rear side of the inner or lower surface of the upper plate 24 to be separated from each other by a predetermined interval. The projections 50 to 52 have a substantially semicircular cross-section and extend along the longitudinal direction of the housing 12. The circuit board 20 is arranged in a position wherein its periphery is pressed against the projections 50 to 52 and positioned. More specifically, one long side of the rectangular circuit board 20, i.e., the upper edge is brought into contact with the projections 51 and 52 on the upper plate 24 of the housing main 12. At the same time, one short side of the board 20, i.e., the right side edge in Fig. 3, is brought into contact with the projection 50 on the side plate 23. With this arrangement, the circuit board 20 is supported at the three points, and its movements along two transverse directions perpendicular to each other and in the rotational direction are limited. Springs 54 to 56 for pressing the circuit board 20 against the projections 50 to 52 are integrally formed on the rear sides of the inner surface of the side plates 22 and 23 of the housing 12. As shown in Fig. 6, the spring 54 for pressing the circuit board 20 upward is formed, at a position adjacent to the transverse plate 28, on the inner surface of the side plate 23 having the projection 50. The spring 55 for pressing the circuit board 20 upward and the spring 56 for pressing the circuit board 20 toward the opposing side plate 23 are provided, at positions adjacent to the transverse plate 28, on the inner surface of the side plate 22. Various shapes of the springs 54 to 56 can be considered. In this embodiment, each of the springs 54 to 56 is an arch-like projecting piece having one end integrally fixed to the side plate 22 or 23. When the circuit board 20 is arranged at a predetermined position to bring the front surface of the flat plate portion 46 of the transparent lid 44 into contact with the rear surface of the transverse plate 28, the springs 54 to 56 are brought into contact with the outer surface of the peripheral portion 48 of the transparent lid 44, thereby pressing the transparent lid 44. At this time, the springs 54 to 56 do not directly press the circuit board 20. However, since the transparent lid 44 is fixed to the circuit board 20, the pressing forces of the springs 54 to 56 act on the circuit board 20 through the transparent lid 44, thereby pressing the circuit board 20 against the projections 50 to 52. The circuit board 20 pressed against the projections 50 to 52 by the springs 54 to 56 does not move in a plane defined by the surface of the circuit board 20. The positions where the projections 50 to 52 are in contact with the circuit board 20 are kept unchanged. For this reason, when the light-emitting element 16 and the light-receiving element 18 are arranged at predetermined positions on the circuit board 20, the predetermined position being previously determined on the basis of the contact points as reference points, the light-emitting element 16 and the light-receiving element 18 are always arranged on the central axes of the corresponding sleeves 30 and 31, respectively, at the time of mounting the circuit board 20. As described above, the module 10 according to the present invention has the cover 14. The cover 14 closes the rear end portion of the housing 12 to hold the circuit board 20. In this embodiment, the cover 14 can be mounted at the rear end portion of the housing 12 by dovetail joints. More specifically, dovetail-like projections 58 and 59 formed on the rear edges of the side plates 22 and 23 of the housing 12 are engaged with dovetail grooves 60 and 61 formed at the corresponding positions on the front surface of the cover 14, thereby joining the cover 14 and the housing 12. At least one (two in this embodiment) spring 62 is integrally formed on the front surface of the cover 14. When the cover 14 is mounted on the housing main 12, the springs 62 press the rear surface of the circuit board 20 forward. As a result, the circuit board 20 is pressed forward, and the front surface of the flat plate portion 46 of the transparent lid 44 is brought into tight contact with the rear surface of the transverse plate 28, thereby arranging the circuit board 20 and the transverse plate 28 almost parallel to each other. With this arrangement, the circuit board 20 is prevented from being separated from the springs 54 to 56 of the side plates 22 and 23, and at the same time, a deviation of the optical axis is prevented. The lead pins 42 of the circuit board 20 externally extend from a gap between the cover 14 and the bottom plate 26 of the housing 12 to enable connection to the external circuit. As described above, when the optical module of this embodiment is used, the circuit board 20 is accurately positioned with respect to the housing 12. For this reason, the light-emitting element 16 and the light-receiving element 18 are coaxially arranged with the corresponding sleeves 30 and 31 and the internal lenses 38 and 39, respectively. As is apparent from the above description, when the circuit board 20 having the light-emitting element 16, the light-receiving element 18, the electronic components, and the transparent lid 44 fixed thereon is arranged at a predetermined position in the housing 12 and held by the springs 54 to 56, and the cover 14 is mounted, the optical module of the present invention can be easily manufactured. When the dimensional precision of an actually assembled optical module was checked, it was confirmed that the dimensional precision among the sleeves, the lenses, and the phototransducer elements was ±15 µm or less in a plane perpendicular to the optical axes and ±50 µm or less in a direction parallel to the optical axes. This falls within a tolerance of the optical coupling efficiency when a quartz fiber (graded-index type, core diameter: 62.5 µm) is coupled to a light-activated element. In case the circuit board 20 is made of a ceramic, it is common that a large ceramic plate is divided along a predetermined line, thereby forming the circuit board 20. Generally, the periphery of the circuit board 20 obtained in this manner is not polished. Therefore, the size of the circuit board 20 varies for each product, and each edge does not form a perfect line. For this reason, it becomes difficult to accurately mount the light-emitting element 16 and the light-receiving element 18 at predetermined positions on the circuit board 20. If the light-emitting element 16 and the light-receiving element 18 are inaccurately mounted on the circuit board 20, the light-emitting element 16 and the light-receiving element 18 are not aligned with the corresponding sleeves 30 and 31 even if the circuit board 20 is arranged at a predetermined position in the package main body 12, as a matter of course. In the present invention, the light-emitting element 16 and the light-receiving element 18 may be mounted on the circuit board 20 using an apparatus as shown in Fig. 9. The light-activated element mounting apparatus in Fig. 9 includes a board supporting table 64 having a flat upper surface on which the circuit board 20 is to be mounted. Columnar pins 70 to 72 are mounted on and perpendicularly extend from the upper surface of the board supporting table 64 in substantially the same layout as that of the positioning projections 50 to 52 in the housing 12. More specifically, the pins 70 to 72 are arranged such that points 50a, 51a, and 52a in Fig. 6 match points 70a, 71a, 72a in Fig. 9, respectively. These points are ones with which the circuit board 20 is brought into contact. Therefore, when the circuit board 20 rests on the board supporting table 64 such that a long side 20a and a short side 20b of the circuit board 20 are brought into contact with the pins 70 to 72, the contact points of the pins 70 to 72 match the contact points of the positioning projections 50 to 52, respectively. Using the contact points as reference points, the light-emitting element 16 and the light-receiving element 18 are arranged on the circuit board 20 at positions determined in advance with respect to the reference points. In this case, upon mounting the circuit board 20 in the package main body 12, the light-emitting element 16 and the light-receiving element 18 are arranged at predetermined positions in the housing 12 regardless of the shape of the circuit board 20. When the light-emitting element 16 and the light-receiving element 18 are to be actually mounted on the circuit board 20, first of all, the circuit board is rested on the board supporting table 64. Thereafter, forces as indicated by arrows 74 to 76 are caused to act on the circuit board 20, thereby holding the circuit board 20 on the board supporting table 64. The light-emitting element 16 and the light-receiving element 18 are fixed at predetermined positions using the contact points of the pins 70 to 72 as the reference points. When the light-emitting element 16 and the light-receiving element 18 are to be fixed, a suitable manipulator such as a robot arm having a collet at the distal end thereof is preferably used. If the dimensional precision of the circuit board 20 is high, the mounting positions of the light-emitting element 16 and the light-receiving element 18 can be easily specified without using the above-described phototransducer element mounting apparatus. In this case, bottomed holes (not shown) can be formed at the element mounting positions on the circuit board 20 in advance, and the phototransducer elements 16 and 18 can be fitted in the holes, thereby accurately positioning the phototransducer elements 16 and 18. A ground electrode or a lead electrode for inputting/outputting an electrical signal may be provided by metallization or the like on the inner wall and the bottom surface of the bottomed hole. Metallized portions may be formed to be used as the mounting positions of the phototransducer elements 16 and 18 without forming the bottomed holes. The preferred embodiment of the present invention has been described above. The present invention is not limited to this embodiment, of course. The optical module of the above embodiment is a module used for both transmission and reception, and the light-emitting element 16 and the light-receiving element 18 are arranged on one circuit board 20. However, the present invention can also be applied to an optical module having only one function of transmission or reception. In the above embodiment, the springs 54 to 56 press the circuit board 20 through the transparent lid 44. However, the springs may directly press the circuit board 20. In the above embodiment, the springs 54 to 56 for pressing the circuit board 20 against the positioning projections 50 to 52 are formed on the housing 12. However, as in an optical module shown in Figs. 10 to 13 , these springs may be arranged on the remaining members constituting the housing. In the optical module in Figs. 10 to 13, a space portion 80 for arranging a circuit board 20' is formed at the central portion of a housing 12' (Fig. 12). A cover 14' is mounted, from the lower side of the circuit board 20' and main body 12' (Fig. 13). In this arrangement, as shown in Fig. 13, a spring 56' for pressing the circuit board 20' against a positioning projection 50' on a side plate 23' of the housing 12' is provided on the inner surface of a side plate 22', as in the above embodiment. However, springs 55' and 56' for pressing the circuit board 20' against positioning projections 51' and 52' on the inner surface of the upper plate 24 are provided to the cover 14'. In this case, when the cover 14' is mounted, the circuit board 20' is simultaneously completely pressed against the projections 50' to 52', so the optical module can be more easily assembled. As has been described above, according to the present invention, the sleeves and the housing are integrally formed of a plastic, and the phototransducer elements are fixed on the circuit board in advance. With this arrangement, the optical module can be assembled in a number of manufacturing steps smaller than that of the prior art. Therefore, the optical module can be provided at lower cost. In addition, the housing is formed of a plastic, so mass production can be achieved. Furthermore, the circuit board is supported at the three points. This arrangement can cope with circuit boards having various shapes and sizes, so that a circuit board can always be supported at predetermined reference points. Therefore, when the phototransducer elements are arranged at predetermined positions corresponding to the reference points, the phototransducer elements, the sleeves, and the lenses can be coaxially arranged. From the invention thus described, it will be obvious that the invention may be varied in many ways. The basic Japanese Application No. 5-245479 filed on September 30, 1993 is hereby incorporated by reference.

Claims: An optical module (10) for receiving and holding a connector plug connected to an end portion of an optical fiber, comprising: an elongate, open-ended housing (12;12') divided by an inner transverse wall (28) into a front receptacle for receiving and holding said optical fiber connector plug and a rear receptacle or recess (40;80), said transverse wall being provided with a through-aperture (33) communicating between the two receptacles; a sleeve (30,31) projecting integrally from the front face of said transverse wall towards the housing front open end whilst surrounding said through-aperture, so as to receive said optical fiber end portion when said connector plug is held in said front receptacle; a phototransducer device (16,18,20;20') to be held in said housing rear receptacle or recess so as to have its active area facing said through-aperture in said transverse wall; and a cover (14;14') for closing at least the open end of said rear receptacle or recess holding said phototransducer device; characterized in that said housing (12;12') together with said sleeve (30,31) is made of molded plastics material; a condenser lens (39) is coaxially arranged in said sleeve; said phototransducer device (16, 18, 20;20') comprises a circuit board (20;20') and a phototransducer element (16,18) fixed at a predetermined position on said circuit board, said circuit board being adapted to be held in said rear receptacle or recess substantially parallel to said transverse wall; three projections (50,51,52;50',51',52') are formed integrally on the inner surface of said housing rear receptacle or recess so as to enable the periphery of said circuit board to be brought into contact with said projections to position said circuit board with its phototransducer element facing said through-aperture; and spring means (54,55,56;54',55',56') are formed integrally on the inner surface of said housing rear receptacle and/or of said cover, at locations thereof substantially opposite to the projections, to press said periphery of said circuit board against said projections. A module according to claim 1, wherein said circuit board (20; 20') is substantially rectangular, one (50; 50') of said projections is located to be contacted by a first side of said circuit board, and the remaining two (51, 52; 51', 52') of said projections are located to be contacted by a second side of said circuit board, which is adjacent to said first side. A module according to claim 2, wherein said elongate housing (12; 12') is an elongate, open-ended box of a substantial rectangular prism shape, said one (50; 50') of said projections is formed on the inner surface of one side wall (23; 33') of said elongate box and said remaining two (51, 52; 51', 52') of said projections are formed on the inner surface of the upper wall (24; 24') of said elongate box. A module according to claim 1, wherein said spring means (54, 55, 56; 54', 55', 56') comprises a plurality of springs for said circuit board against said projections. A module according to claim 3, wherein said circuit board is substantially rectangular, said spring means (54, 55, 56) comprises a spring (56) formed integrally on the inner surface of the other side wall (22) opposite to said one side wall (23) of said housing to press said circuit board (20) against said one (50) of said projections provided on said one side wall (23) of said housing (12), and a spring (54, 55) formed integrally on the lower part of the inner surface of each of said two side walls (22, 23) of said housing to press said circuit board (20) against said remaining two (51, 52) of said projections provided on said upper wall (24). A module according to claim 1, wherein said cover (14) adapted to contact, when mounted, the rear surface of said circuit board (20) arranged in said rear compartment or recess. A module according to any one of the claims 1 to 4, wherein said rear compartment is provided in the lower part of its wall, with a transverse through-slit (80) through which the circuit board (20') is to be inserted, and said cover (14') is adapted to also close, when mounted, said through-slit (80). A module according to claim 7 when appended to claim 4, wherein said spring means (54', 55', 56') comprise a spring (56') formed integrally on the inner surface of the other side wall (22') opposite to said one side wall (23') of said housing (12') to press said circuit board (20') against said one (50') of said projections provided on said one side wall (23'), and two distant springs (54', 55') formed integrally on the inner surface of said cover (14') to press said circuit board (20') against said remaining two (51', 52') of said projections provided on said upper wall (24') of said housing (12'). A module according to claim 1, wherein a transparent lid (44) is fixed to the front face of said circuit board (20; 20') to cover an electronic circuit and said phototransducer element (16, 18) on said circuit board, and said spring means (54, 55, 56; 54', 55',56')causes a pressing force to act on said circuit board through said transparent lid. A module according to claim 1 , wherein said optical module is a transmission module having a light-emitting element (16) as said phototransducer element. A module according to claim 1, wherein said optical module is a reception module having a light-receiving element (18) as said phototransducer element. A module according to claim 1, wherein said optical module is a transmission/reception module having a lightemitting element (16) and a light-receiving element (18) as said phototransducer element. A module according to claim 1, wherein a plurality of grooves (34) are formed in the inner surface of said sleeve (30, 31), which extend in a longitudinal direction and are circumferentially spaced to one another. A method of mounting a phototransducer element (16, 18) at a predetermined position on a circuit board (20; 20'), in view of using said circuit board thus provided with said phototransducer element in an optical module (10) as defined in claim 1, said method comprising the steps of: providing a board supporting table (64) having three positioning pins (70, 71, 72) mounted on main surface thereof in substantially the same arrangement as that of said three projections (50, 51, 52; 50', 51', 52') on the inner surface of said elongate housing (12, 12') of said optical module (10) ; resting the circuit board (20, 20') on said main surface of said board supporting table; pressing said circuit board such that the periphery of said circuit board is brought into contact with all said pins; and defining contact points of said pins as reference points; and fixing said phototransducer element (16, 18) at a position predetermined with respect to the contact points between said pins and said circuit board, which contact points serve as reference points. A method according to claim 14, wherein said circuit board (20, 20') is substantially rectangular, one (70) of said pins is located to be contacted by a first side of said circuit board, and the remaining two (71, 72) of said pins are located to be contacted by a second side of said circuit board, which is adjacent to said first side. A method according to claim 14, wherein said phototransducer element is a light-emitting element (16). A method according to claim 14, wherein said phototransducer element is a light-receiving element (18).

Inventors: KURASHIMA HIROMI, KURASHIMA, HIROMI, KURASHIMA, HIROMI, C/O YOKOHAMA WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1994
Main classification: G02B6
IPC codes: G02B6